This study is designed to determine whether flushing the Groshong catheter with heparinized saline once a week instead of normal saline alone will prevent blood clotting in the catheter. Patients and nurses at the Clinical Center have reported observing retrograde blood in the Groshong catheter These reports led the principal investigator to examine 28 Groshong catheters at the time of removal. All 28 catheters were found to have clotted blood within the catheter, clot hanging from one or both of the valves, and/or bloody saline in one or both catheter lumens. All the observed catheters had been flushed weekly with normal saline. This study obtained data from 23 patients who flushed their Groshong catheters weekly with heparinized normal saline (2.5 ml 5,000 units/ml). Of these 23 catheters flushed with heparin, 12 were explanted and 11 remained in place at the time of this report. Eight catheters were made available for examination. In contrast to the saline-flushed groups, none of the heparin-flushed catheters had adherent clot (P< 0.0001); the presence of intraluminal clot was also significantly less frequent in the heparin flush group (p<0.0078). Finally, improvement in catheter function, as measured by the use of urokinase for catheter occlusion, was found in the heparin-flushed group (P< 0.0006). The saline-flushed group required the use of urokinase to reestablish catheter patency at a rate of one vial of urokinase for every 36 catheter days. In contrast, the heparin- flushed group requirements for urokinase was one vial for every 270 catheter days. These findings have clinical significance for improved catheter function and patients' ability to complete treatment protocols. In addition, significant cost benefits appear to be related to improved catheter function and decreased urokinase use in heparin-flushed catheters. The findings of this study served as the basis for a prospective, randomized clinical trial that compared the frequency of malfunction in catheters flushed with saline or heparinized saline.